1. Field of the Invention
This invention relates to methods for measuring surface treatment coverage, and more particularly, to such methods for measuring shot peening coverage. Such methods generally employ an automated computer analysis of the peened surface coverage by analyzing surface line traces to determine when a particular surface has been surface hardened enough.
2. Description of the Related Art
Under normal shot peening conditions, it is desirable to expose the substrate or work surface to the shot stream for a sufficient time to achieve 100% surface coverage, i.e. sufficient exposure to fully cover the surface with impact dimples. Insufficient coverage has obvious adverse consequences. If the local compressive zones due to individual shot strikes do not merge into a continuum that fully covers the surface with a compressive layer, locally unprotected regions will exist where surface flaws can grow into cracks.
On the other hand, shot peening related damage is not necessarily caused only by broken or deformed shot, but rather excessive cold work may play a significant part in the damage process. The cold work sustained by the material is a function of both coverage and intensity, as well as, shot size. To minimize damage due to excessive cold work, or prevent overly worked parts from entering service, it is desirable to measure the coverage. Furthermore, for uniform flat surfaces it is relatively easy to set and control the exposure time needed to maintain the desired coverage condition. However, on surfaces with features, such as inside corners where reflections cause multiple strikes, it may be difficult to avoid excessive coverage, in some cases to the point where surface distress may occur. Therefore, for these reasons, it is necessary that a nondestructive system to measure cold work coverage be provided.
It is apparent from the above that there exists a need in the art for a system for measuring shot peening coverage which will not destruct the substrate in order to complete the evaluation, but which will evaluate the coverage on the substrate surface in a manner which provides a full and complete analysis of the coverage. It is a purpose of this invention, to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.